JavaScript Best Practices

gistfile1.js

1. Use === and !== Instead of == and !=

2. Eval = Bad

3. Do not use short-hand, for example: omitting curly braces and semi-colons

4. Utilize http://www.jslint.com/

5. Place Scripts at the Bottom of Your Page

6. Declare Variables Outside of the For Statement

7. The Fastest Way to Build a String - Using native methods (like join()), regardless of what’s going on behind the abstraction layer, is usually much faster than any non-native alternative.

8. Reduce Globals

9. Comment Your Code

10. Embrace Progressive Enhancement. Always compensate for when JavaScript is disabled.

11. Do not Pass a String to "SetInterval" or "SetTimeOut"

12. Do not Use the "With" Statement, use var object

13. Use {} Instead of New Object()

14. Use [] Instead of New Array()

16. Optimize loops. One of the most common mistake is to read the length attribute of an array at every iteration.
var names = ['George','Ringo','Paul','John'];
var all = names.length;
for(var i=0;i<all;i++){
  doSomeThingWith(names[i]);
}
OR......
var names = ['George','Ringo','Paul','John'];
for(var i=0,j=names.length;i<j;i++){
  doSomeThingWith(names[i]);
}

15. Long List of Variables? Omit the "Var" Keyword and Use Commas Instead

17. Always, Always Use Semicolons

18. "For in" Statements. When looping through items in an object, you might find that you will also retrieve method functions as well. In order to work around this, always wrap your code in an if statement which filters the information.

19. Use Firebug "Timer" Feature to Optimize Your Code
function TimeTracker(){  
 console.time("MyTimer");  
 for(x=5000; x > 0; x--){}  
 console.timeEnd("MyTimer");  
}

21. Self-Executing Functions

(function doSomething() {  
   return {  
      name: 'jeff',  
      lastName: 'way'  
   };  
})();

22. Raw JavaScript Can Always Be Quicker Than Using a Library. jQuery "each" method is great for looping, but using a native "for" statement will always be an ounce quicker.

23. Crockford JSON.Parse
var response = JSON.parse(xhr.responseText);  
var container = document.getElementById('container');  
for(var i = 0, len = response.length; i < len; i++) {  
  container.innerHTML += '<li>' + response[i].name + ' : ' + response[i].email + '</li>';  
}

24. Remove "Language"
<script type="text/javascript" language="javascript">  
...  
</script>